The present invention relates to a canister which can be used as a fuel vapor processing device for trapping fuel evaporated from a fuel tank of a motor vehicle, and burning the trapped fuel in an internal combustion engine at the time of operation.
As is well known, a canister is used as a fuel vapor treatment device or evaporative emission control device for restraining emission of fuel vapor, such as gasoline vapor, generated in a fuel tank in the stop state of a vehicle, for example. The canister is arranged to trap or adsorb fuel vapor with an adsorbing material or adsorbent such as activated carbon, and to purge or release the trapped fuel with a stream of fresh air introduced from an air port, to supply the fuel component into an intake passage of an engine for combustion disposal in the engine during operation of the engine. By this purge operation to release the adsorbed fuel vapor, the activated carbon can regain the power of adsorption and repeat operation of adsorbing fuel vapor.
In such a canister using activated carbon, the temperature in the canister becomes higher because of exothermic reaction, and the resulting temperature increase tends to deteriorate the adsorbing performance. In the case of desorption of fuel component, on the other hand, the reaction is endothermic. Therefore, the temperature of the canister becomes lower and the desorbing performance tends to become poorer.
To meet this problem, a patent document 1 (JP 62-38468 U) proposes a canister utilizing granular polymer or substance made of giant molecules, mixed with granular activated carbon. A patent document 2 (JP 64-36962 A) proposes activated carbon particles containing heat accumulating solid fillers having a specific heat greater than that of the activated carbon. A patent document 3 (JP 10-339218 A) and a patent document 4 (JP 2006-207485 A) propose the use of heat accumulating particles having higher heat conductivity and greater heat capacity, attached to the surfaces of activated carbon. A patent document 5 (JP2005-233106A) proposes a mixture of particles of adsorbing material and particles of heat storing or accumulating material molded by adding a binder to powder of micro capsules encapsulating a phase-change material for absorbing and releasing latent heat in dependence on temperature change.